This invention relates, generally, to a differential signal detector circuit and, specifically, to a floating base point wave form cutoff differential signal detector circuit.
The best-known circuit that has been used to detect a differential signal is preset to a maximum allowable differential signal value or base point and generates the detection signal when the differential signal is larger than the preset base-point value. A typical differential signal detector of this type has an operational amplifier with its positive pole (operational input) connected to receive the differential signal and its negative pole (operational input) connected to two voltage-dividing resistors to preset the base-point value described above.
Such a differential signal detector circuit produces false detection signals easily in many applications. For example, in a burglar alarm system using a microwave or ultrasonic sensor for generating the differential signal, changes in the sensed environment, from changed furniture or a blowing curtain, for example, change the differential signal from the sensor and make the circuit generate unpredictable detection signals. The changes described above occur frequently in a house, for example, because the furniture is regularly changed and window opening is necessary, so such a burglar-alarm system in a house under these conditions will make wrong detection signals easily. Besides, other conditions, such as a moth close to the sensor, can lead to the same result, too.